GaN-containing semiconductor structure

ABSTRACT

A method for forming a GaN-containing semiconductor structure is provided. The method comprises a substrate is provided, a nucleation layer is formed above the substrate, a diffusion blocking layer is formed above the nucleation layer, a strain relief layer is formed above the diffusion blocking layer, and a semiconductor layer is formed above the strain relief layer, in which the diffusion blocking layer is deposited on the nucleation layer such that the diffusion blocking layer can prevent the impurities out-diffusion from the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a GaN-containing semiconductorstructure, more particularly to a GaN-containing semiconductor structurefor GaN electronic device and the manufacturing method thereof.

2. Description of the Prior Art

Generally speaking, as for the manufacturing process of GaN-containingelectronic device, high quality aluminum nitride (AlN) buffer layer isrequired to reduce the current leakage problem of electronic device. TheAlN buffer layer can prevent the oxygen out-diffusion from thesubstrate, particularly from the sapphire substrate. In addition, theAlN buffer layer can also prevent the silicon (Si) diffusing from thesilicon substrate or silicon carbide substrate into the GaN material.

However, due to the rough surface of AlN buffer and the large latticeconstant mismatch between AlN and GaN material, GaN layer grown on AlNbuffer will also suffer from having rough surface morphology.

In the prior art, during the growth process of AlN, the ammonia (NH3) isadjusted by entering the growth chamber periodically. The diffusiondistance of aluminum atom on material surface can be increased by themethod, and the surface of formed AlN will be a smooth surface. However,this method is complex and the growth control of AlN is difficult. Inaddition, this method will also reduce the growth rate of AlN. There isanother problem that the quick and rapid on/off operation will cause thefailure of the mass flow controller of metal organic chemical vapordeposition (MOCVD) or the mechanical shutter of molecular beam epitaxy(MBE).

In another prior art, other approaches comprise using extreme growthconditions in the MOCVD such as a very high growth temperature (>1200°C.) or a very low group V to group III gases flow ratio (V/III ratio,<10). However, most of the growth reactors cannot provide such hightemperature and low V/III ratio. The extreme growth parameters maybeyond the optimized range of growth conditions designed for most of theMOCVD reactors. As a consequence, the gas flow dynamics in the reactorwill be significantly affected.

Sometime, an AlGaN buffer layer is also used to prevent theout-diffusion problem. However, it may not as effective as the AlN,because the AlGaN has lower bandgap. Thus, the impurity such as oxygenatom in this material will tend to form shallow donor and thus reducethe resistivity of the material. Its capability to trap impurities isalso poorer as compared to AlN. Thus, the impurities may still diffuseinto the GaN layer.

SUMMARY OF THE INVENTION

According to the shortcoming of known art, the main purpose of thepresent invention is to disclose a GaN-containing semiconductorstructure with composite buffer layer, high resistive and smooth surfacemorphology.

Another purpose of the present invention is to utilize low leakagecurrent electronic device process to form a GaN-containing semiconductorstructure.

According to the abovementioned purposes, a method for forming aGaN-containing semiconductor structure is provided by the presentinvention. The method includes a substrate is provided, a nucleationlayer is formed above the substrate, a diffusion blocking layer isformed above the nucleation layer, a strain relief layer is formed abovethe diffusion blocking layer, and a semiconductor layer is formed abovethe strain relief layer, in which the diffusion blocking layer isdeposited on the nucleation layer such that the diffusion blocking layercan prevent the impurities out-diffusion from the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of thisinvention will become more readily appreciated as the same becomesbetter understood by reference to the following detailed description,when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 illustrates the block flow diagram for forming the GaN-containingsemiconductor structure according to the technology disclosed by thepresent invention.

FIG. 2 illustrates the cross-sectional view of GaN-containingsemiconductor structure according to the technology disclosed by thepresent invention.

FIG. 3 illustrates the transmission electron microscope (TEM) diagram ofGaN-containing semiconductor structure according to the technologydisclosed by the present invention.

FIG. 4( a) and FIG. 4( b) illustrates the optical image diagram of theGaN growth structure with the diffusion blocking layer and the strainrelief layer as the buffer layers as well as the GaN growth structurewith a single buffer layer according to the technology disclosed by thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Please refer to FIG. 1. FIG. 1 illustrates the block flow diagram forforming the GaN-containing semiconductor structure according to thetechnology disclosed by the present invention. In FIG. 1, a substrate isprovided in Step 12 first. A nucleation layer is formed above thesubstrate in Step 14. A diffusion blocking layer is formed above thenucleation layer in Step 16. Then, a strain relief layer is formed abovethe diffusion blocking layer in Step 18. Finally, a semiconductor layeris formed above the strain relief layer in Step 20 to complete theGaN-containing semiconductor structure. The GaN-containing semiconductorstructure is suitable for high electron mobility transistor (HEMT) orSchottky barrier diode (SBD). In addition, the metal organic chemicalvapor deposition (MOCVD) is used as the deposition method in theembodiment.

Then, please refer to FIG. 2. FIG. 2 illustrates the cross-sectionalview of GaN-containing semiconductor structure according to thetechnology disclosed by the present invention. In FIG. 2, theGaN-containing semiconductor structure 3 comprises a substrate 30, anucleation layer 32, a buffer layer 34 and a GaN semiconductor layer 36from bottom to top.

In the present invention, the substrate 30 may be the silicon substrate,the silicon carbide substrate or the sapphire substrate. The nucleationlayer 32 is grown on the substrate 30 by the metal organic chemicalvapor deposition (MOCVD). In the embodiment, the deposition temperatureof nucleation layer 32 is from 500° C. to 800° C. and the depositionthickness is smaller than 50 nm. In addition, the nucleation layer 32may be AlN or AlGaN.

Please refer to FIG. 2 again. In the present invention, the buffer layer34 comprises a diffusion blocking layer 342 and a strain relief layer344, in which the diffusion blocking layer 342 is deposited on thenucleation layer 32 and the strain relief layer 344 is deposited on thediffusion blocking layer 342. In an embodiment of the present invention,the deposition temperature of the diffusion blocking layer 342 on thenucleation layer 32 is from 950° C. to 1200° C., and the depositionthickness is from 100 nm to 2000 nm. In this embodiment, the diffusionblocking layer 342 may be AlN, and single AlGaN layer or AlN andmultiple AlGaN.

It has to stated that the III-nitride layers are deposited on thesubstrate 30 at high temperature (up to 1200° C.). The oxygen or siliconout-diffusion phenomenon will be occurred at this high temperaturecondition. If the substrate 30 is the sapphire substrate, due to thesapphire substrate 30 includes Al2O3, the oxygen will diffuse from thesapphire substrate into the GaN semiconductor layer 36, while thesilicon diffuses from the silicon substrate or the silicon carbidesubstrate into the GaN semiconductor layer 36. Then, the diffusionblocking layer 342 formed in the present invention can prevent theimpurities, such as oxygen or silicon diffusing from the substrate 30into the GaN semiconductor layer 36, so as to increase the reliabilityof the semiconductor structure.

In FIG. 2, the strain relief layer 344 is deposited on the diffusionblocking layer 342 at low temperature, such as from 450° C. to 600° C.,and the better deposition temperature is 500° C. In the embodiment, thestrain relief layer 344 is GaN, the deposition thickness on thediffusion blocking layer 342 is from 30 nm to 100 nm.

Then, due to the deposition temperature of the GaN semiconductor layer344 is lower, the GaN semiconductor layer 344 can be considered as thedefective layer. When the GaN semiconductor layer 36 is deposited, dueto higher growth temperature is required, then the growth temperature israised to about 1050° C. When the growth temperature is increasedcontinuously, the recrystallization of the previous formed GaN strainrelief layer 344 will be started, and the strain of lattice constantmismatch between AlN and GaN will be released, then the GaNsemiconductor layer 36 can obtain high quality and smooth surface.Because the diffusion blocking layer 342 traps or blocks the impuritiesdiffused from the substrate 30 to the GaN semiconductor layer 36, sothat the GaN semiconductor layer 36 has high resistive. In theembodiment, the deposition temperature of the GaN semiconductor layer 36is from 950° C. to 1200° C., and the deposition thickness is 1 um to 5um.

Then, please refer to FIG. 3. FIG. 3 illustrates the transmissionelectron microscope (TEM) diagram of GaN-containing semiconductorstructure according to the technology disclosed by the presentinvention. In FIG. 3, it is obviously shown that the strain relief layer344 of the buffer layer 34 has a structure with multiple defects.

Then, please refer to FIG. 4( a) and FIG. 4( b). FIG. 4( a) and FIG. 4(b) illustrates the optical image diagram of the GaN growth structurewith the diffusion blocking layer and the strain relief layer as thebuffer layers as well as the GaN growth structure with a single bufferlayer. FIG. 4( a) shows GaN growth structure with the diffusion blockinglayer 342 and the strain relief layer 344 as the buffer layer 34. FIG.4( b) shows the GaN growth structure with a single AlN buffer layer. Itis obvious that FIG. 4( a) shows smooth surface of GaN growth structureand FIG. 4( b) shows rough surface of GaN growth structure.

Therefore, according to the abovementioned description, the highresistive GaN-containing semiconductor structure for the GaN electronicdevice includes a buffer layer 34 composed of the diffusion blockinglayer 342 and the strain relief layer 344. The material of diffusionblocking layer 342 may be one single AlN layer, or one single AlN layerwith one single AlGaN layer, or one single AlN layer with multiple AlGaNlayers. The material of strain relief layer 344 is the GaN grown at lowtemperature. Although the strain relief layer 344 grown at lowtemperature has many defects, it can mitigate the strain of latticeconstant mismatch between AlN and GaN. When the temperature of thesubstrate 30 is increased, the strain relief layer 344 grown at lowtemperature will recrystallize. The recrystallization will increase thequality of GaN layer 36 effectively. The GaN material with smoothsurface can be grown on the diffusion blocking layer 342 with roughsurface by this growth mode. Meantime, due to the combination of thediffusion blocking layer, the impurities in the GaN can be reduced tominimum, in order to increase the material resistive significantly. Byusing this high resistive GaN material as the buffer layer for highelectron mobility transistor or Schottky barrier diode, the leakagecurrent of electronic device can be reduced effectively, and the powerconversion efficiency of device can be increased.

It is understood that various other modifications will be apparent toand can be readily made by those skilled in the art without departingfrom the scope and spirit of this invention. Accordingly, it is notintended that the scope of the claims appended hereto be limited to thedescription as set forth herein, but rather that the claims be construedas encompassing all the features of patentable novelty that reside inthe present invention, including all features that would be treated asequivalents thereof by those skilled in the art to which this inventionpertains.

What is claimed is:
 1. A method for forming a GaN-containingsemiconductor structure by using metal-organic chemical vapor deposition(MOCVD), comprising: providing a substrate; providing a nucleation layeron the substrate by using metal-organic chemical vapor deposition(MOCVD), wherein a forming temperature of the nucleation layer is from500° C. to 800° C.; providing a diffusion blocking layer on thenucleation layer by using metal-organic chemical vapor deposition(MOCVD), wherein the forming temperature of the diffusion blocking layeris from 950° C. to 1200° C.; providing a strain relief layer on thediffusion blocking layer by using metal-organic chemical vapordeposition (MOCVD), wherein the forming temperature of the strain relieflayer is from 450° C. to 600° C.; and providing a semiconductor layer onthe strain relief layer by using metal-organic chemical vapor deposition(MOCVD), wherein the forming temperature of the semiconductor layer isfrom 950° C. to 1200° C.
 2. A GaN-containing semiconductor structureformed by using metal-organic chemical vapor deposition (MOCVD),comprising: a substrate; a nucleation layer on the substrate, whereinthe nucleation layer is AlN layer; a diffusion blocking layer on thenucleation layer, wherein the diffusion blocking layer is selected fromthe group consisting of a single AlN layer, the single AlN layer with asingle AlGaN layer, the single AlN layer with multiple AlGaN layers,wherein the forming temperature of the diffusion blocking layer is from950° C. to 1200° C.; a strain relief layer on the diffusion blockinglayer, wherein the strain relief layer is GaN, and a thickness of thestrain relief layer is from 30 nm to 100 nm, the forming temperature ofthe strain relief layer is from 450° C. to 600° C.; and a semiconductorlayer on the strain relief layer, wherein the forming temperature of thesemiconductor layer is from 950° C. to 1200° C.